1. Field of the Invention
The invention relates in general to a safety valve apparatus and a method for its installation and replacement of valve elements. Specifically, the invention relates to a production well valve apparatus which functions as a blowout preventer. More specifically, the invention is directed for use on offshore production platforms where a plurality of producing oil wells are disposed in close proximity to one another where there is an emergency need to simultaneously shut in all the producing wells rapidly safely, reliably, and economically while facilitating rapid resumption of production after the emergency has passed.
2. Description of the Prior Art
On marine production platforms there are often many producing wells in close proximity to one another. Each of the wells typically has a production wellhead from which production tubing extends from the well. The wellhead typically has a production or "Christmas" tree connected to it for controlling the gas or fluid flowing in the production tubing during production of the well. A master gate valve disposed in each production tree may be closed to shut off flow from the well, but such gate valves may be difficult to close rapidly during an emergency due to their location and indeed may not be available as where the production tree is removed from the wellhead during workover of the well.
Downhole safety valves may also be provided in each of the producing wells. There is always the danger that a downhole safety valve may not be operable or in place during workover of the well. As indicated above, during workover, the production tree may have been removed in order to install a blowout preventer stack atop the production wellhead for control of the well during workover. Such a blowout preventer stack is of the kind used typically in drilling operations and includes one or more ram-type blowout preventers and an annular blowout preventer. Until the blowout preventer is installed on the production wellhead and connected to its controls, well control in the past for the well has depended upon remotely installed plugs in the well. Such plugs have not always been reliable.
During an emergency on a offshore platform, for example where a fire or leaking gas or fluid from one production tree endangers all of the wells and indeed the platform itself, there has developed the need for an apparatus and method for its installation and refurbishing which may be used to rapidly close off the flow path of the production tubing in each of the wells.
As indicated above, a shear ram blowout preventer similar to those used in marine blowout preventer stacks for drilling operations could be a candidate for satisfying such a need. The use of a shear ram blowout preventer has a major disadvantage in that the tubing above the tubing hanger must be replaced after it has been sheared before production can be resumed. Shear ram blowout preventers crush the production tubing which must be replaced before the well can be put back into operation. In order to replace the crushed tubing, the production tree must be removed and a drilling blowout preventer and rig installed in order to remove the damaged tubing and replace it with new tubing.
Another disadvantage of using a shear ram blowout preventer similar to that used in drilling operations is that after the preventer crushes and shears the tubing, the well can only be controlled by pumping mud into it to control the pressure in the well. A plug typically cannot be installed through the tubing which has been crushed during the shearing by the preventer.
Another disadvantage of using a shear ram blowout preventer as a production well blowout preventer is that a typical shear ram is a large, bulky device requiring a large amount of platform space. Such space comes at very high cost on production platforms.
There have been prior attempts to find production well blowout preventers which satisfy the needs identified above. For example, U.S. Pat. No. 3,716,068 to Addison discloses a valve apparatus for controlling flow through a flow line and is adapted for use in a producing oil well. The valve apparatus includes a housing adapted to be mounted about the flow line and a flow blocking means mounted in the housing for movement toward the flow line. A boring tip on a wedge-like boring member is used to bore through a soft plug of the housing and then to establish a hole in the production tubing itself. The wedge-like flow blocking member bores and eventually shears the production tubing, thereby interrupting the flow in the production tubing. Protective seals are provided in the housing of the apparatus in order to protect the boring means from contamination.
In U.S. Pat. No. 1,851,894 issued to Clough, a control device for oil or gas wells is illustrated in which a boring apparatus drills through a protective seal of an annulus and through a production tubing thereby interrupting any flow which happened to be in the annulus and in the production tubing.
The patents mentioned above represent but two attempts over the years to provide shearing and sealing apparatus in order to interrupt the flow in a producing oil well. There has existed a continuing need to provide a safety valve adapted for controlling flow in production tubing in a producing well which is capable of automatic operation on a single well where a dangerous hazard has developed and on all wells on a producing platform. It is a major object of this invention to provide a producing well blowout preventer in which only a small element is replaced after the valve has closed and which does not require that the production tree be removed in order to replace the disposable part.
It is a further object of the invention to provide a safety valve in a producing oil or gas well which can be immediately put back into production after the valve has been closed and in which the valve might be put into its ordinary standby condition at a later time.
It is another object of the invention to provide a safety valve for use in a producing oil well in which after the safety valve has been actuated and the well put back into production, full access to the well is available into the production tubing for killing the well with drilling fluid and the like, setting plugs, etc.
It is a further object of the invention to provide a production well blowout preventer in which the seals and working mechanism of the preventer are isolated from the fluids flowing through the production line.
It is a further object of the invention to provide a production well blowout preventer which may be pressure tested to full working pressure after it has been actuated and prior to the removal of the production tree.
It is a further object of the invention to provide a punch out tube for the valve in which a middle member of the tube may be easily and cleanly displaced from upper and lower members fixed in the valve by ramming its side.
It is a still further object of the invention to provide a blowout preventer and method for its installation on production wells.
It is a still further object of the invention to provide a production well blowout preventer and a method for replacing a punch out tube in the preventer after the preventer has been actuated and the well put back into production without the necessity of removing the production tree above the preventer.